1. Field of the Invention
The present invention relates to a method for producing an electron-emitting device, a method for producing an electron source, and a method for producing an image-forming apparatus.
2. Related Background Art
Examples of the surface conduction electron-emitting devices include those disclosed in M. I. Elinson, et al., "The Emission of Hot Electrons and the Field Emission of Electrons From Tin Oxide Radio Eng. and Electronic Phys., 10, 1290 (1965), and so on.
The surface conduction electron-emitting devices utilize such a phenomenon that electron emission occurs when electric current is allowed to flow in parallel to the surface in a thin film of a small area formed on a substrate. Examples of the electron-emitting devices reported heretofore include those using a thin film of SnO.sub.2 by Elinson et al. cited above, those using a thin film of Au G. Dittmer: Electrical Conduction and Electron Emission of Discontinuous Thin Films, Thin Solid Films, 9, 317 (1972), those using a thin film of In.sub.2 O.sub.3 /SnO.sub.2 [M. Hartwell and C. G. Fonstad, "Strong Electron Emission From Patterned Tin-Indium Oxide Thin Films," International Electron Devices Meeting, 519, (1975)], those using a thin film of carbon [Hisashi Araki et al.: "Electroforming and Electron Emission of Carbon Thin Films," Journal of the Vacuum Society of Japan, 26, No. 1, p22 (1983)], and so on.
A typical example of these electron-emitting devices is the device structure of M. Hartwell cited above, which is schematically shown in FIG. 19. In FIG. 19, an electrically conductive, thin film 4 is formed on a substrate 1. The electrically conductive, thin film 4 is, for example, a thin film of a metallic oxide formed by sputtering in an H-shaped pattern and an electron-emitting region 5 is formed therein by an energization operation called energization forming. In the drawing the gap L between the device electrodes is set to 0.5 to 1 mm and the width W' to 0.1 mm.
The surface conduction electron-emitting devices described above have an advantage of allowing the capability of readily forming an array of many devices across a large area because of their simple structure and easy production. A variety of applications have been studied heretofore in order to take advantage of this feature. For example, they are applied to charged beam sources, image-forming apparatus (display devices), and so on. An example of the application to formation of an array of many surface conduction electron-emitting devices is, as described below, an electron source comprised of a lot of rows, each row being formed by arraying the electron-emitting devices in parallel and connecting both ends of the individual devices by wires (which will also be referred to as common wires). Particularly, as image-forming apparatus (display devices) or the like, the flat panel type image-forming devices (display devices) using liquid crystal are becoming widespread while replacing the CRTs, but they had problems including the need to have a back light, because they were not self-emission type devices. There have been, therefore, desires for development of self-emission type image-forming devices (display devices). An example of self-emission type image-forming devices (display devices) is an image-forming apparatus, which is an image-forming device (display device) constructed in the form of a combination of an electron source having an array of many surface conduction electron-emitting devices with a fluorescent member for emitting visible light upon reception of electrons emitted from the electron source (for example, U.S. Pat. No. 5,066,883).
In order to produce the large-area electron source substrate and the image-forming apparatus at low cost, it is necessary to decrease the cost of the members used therein. For this reason, a conceivable measure is to use as a substrate an alkali-containing glass such as soda lime glass or the like, which is an inexpensive material.
However, while such alkali-containing glasses were inexpensive on one hand, Na ions easily move, which sometimes posed a problem on the other hand.
For example, U.S. Pat. No. 3,896,016 discloses the problem of Na ions in the application of soda lime glass to the substrate of the liquid crystal display devices. In this application the electrodes are placed on both front and back surfaces of soda lime glass and an electric field is applied at the same time as heating. This operation decreases Na ions in one surface of the soda lime glass, so as to suppress influence thereof to the liquid crystal.
Japanese Laid-open Patent Application No. 9-17333 discloses a problem in the surface conduction electron-emitting device where on a glass substrate containing an alkali such as Na or the like, the device electrodes are formed with a paste containing sulfur and an organometal. Specifically, the Japanese application discloses that the aforementioned paste is printed and baked on the substrate of alkali-containing glass such as soda lime glass or the like whereby a compound containing Na and sulfur is deposited on the surface of the device electrodes. Further, the Japanese application also discloses that this compound makes an unstable electrical connection between the conductive film and the device electrodes. Disclosed as a means for solving it is a process having steps of forming the device electrodes, thereafter cleaning them together with the substrate, and then forming the electroconductive film thereon.
As described above, various means and ideas are often required where the alkali-containing glass (particularly, soda lime glass) is applied to electron devices.
FIG. 22A and FIG. 22B are schematic diagrams to show a conventional surface conduction electron-emitting device. FIG. 22A is a schematic plan view of the device and FIG. 22B is a schematic, sectional view of FIG. 22A. In the surface conduction electron-emitting device, the electroconductive film 4 on which an electron-emitting region 5 is placed is formed in contact with the surface of the substrate 1.
FIGS. 23A to 23D are schematic diagrams to show a method of producing the surface conduction electron-emitting device described above. The surface conduction electron-emitting device is made, for example, as follows.
First, electrodes 2, 3 are formed on the substrate 1 (FIG. 23A).
Next, the electroconductive film is formed so as to make a connection between the electrodes 2, 3 (FIG. 23B). The electroconductive film is formed after formation of the electrodes 2, 3 in this example, but there are also cases where the electrodes are formed after formation of the electroconductive film.
Subsequently, an energization forming step is carried out to energize the electroconductive film 4. The energization method is, for example, a method for energizing the electroconductive film 4 by applying such a voltage that a potential of one electrode out of the pair of electrodes described above becomes higher than a potential of the other electrode. This energization forms a small gap 11 in the conductive film (FIG. 23C).
Further, preferably, an energization activation step to energize the electroconductive film, similar to the above-stated forming step, is carried out in such a state that the region near the aforementioned gap part is in contact with an atmosphere in which an organic substance is present. This step is to form a carbon film 10 on the substrate in the gap 11 and on the electroconductive film 4 near the gap (FIG. 23D). The activation step results in forming a second gap 12 of the carbon film narrower than the gap 11, in the gap 11 formed by the aforementioned forming. The voltage applied in this activation step is preferably set to a voltage higher than the voltage applied in the above forming step in order to obtain the carbon film with higher quality.
The electron-emitting region 5 is formed through the above steps.